1. Field of the Invention
The present invention relates to a sheet conveyance apparatus for use in an image forming apparatus, and more particularly to a sheet conveyance apparatus having a mechanism for flexibly controlling an interval between sheets for use in a sheet reversing unit of an image forming apparatus.
2. Discussion of the Background
Against a background in which an amount of data used in business operation is increasing, there has been a growing demand to reduce an amount of paper used for printing such increased data. As a solution, double-sided image forming is performed so that the amount of paper used for printing can be reduced to cut cost. For an image forming apparatus to have a double-sided image forming function, a mechanism for reversing a sheet is required for transferring image information to two sides of the sheet by using a single transfer unit or a series of transfer units. Many sheet reversing units adopt a switchback mechanism for reversing a sheet having an image formed on one side thereof while the sheet is conveyed. For such a sheet reversing unit to successively reverse a plurality of sheets, a conveyance path and an interval between sheets need to be long enough for performing a switchback operation.
On the other hand, there has also been growing demand for increases in speed and productivity of image forming. Therefore, is it difficult for an image forming apparatus to have a conveyance path having a length long enough for reversing a sheet, while at the same time having enough of an interval between sheets in order to archive an increase in image forming speed. Additionally, the trend in the image forming apparatus industry is towards reducing the size of the image forming apparatus.
Further, efforts for improving the productivity of image forming, which is represented by a number of sheets on which image forming is performed in a unit time, have been made by not only increasing the speed of conveying a sheet but also reducing the interval between sheets. Therefore, a sheet needs to be reversed in an increasingly shorter period of time.
In recent years, along with information digitalization, interleaf control for double-sided image forming has been developed. In an interleaf control operation, a first image forming is successively performed on first sides of a plurality of sheets while the sheets are conveyed into a reverse path after the images are formed. Then, image forming is alternately performed on second sides of the sheets having the images formed on the first sides and newly supplied sheets.
A background sheet conveyance apparatus includes two driving sources independently provided for conveying a sheet into a reverse system and for supplying a sheet having an image formed on one side thereof so that productivity can be improved with a low-cost configuration.
Another background sheet conveyance apparatus includes two motors configured to independently operate. One of the two motors serves as a driving source for conveying a sheet for a discharge operation. The other serves as another driving source for conveying a sheet for a double-sided image forming operation.
Further recently, non-stack interleaf control for double-sided image forming has been in use. In a non-stack interleaf control operation, a sheet having an image formed on one side thereof is supplied for image forming on another side thereof without putting the sheet in an intermediate stack tray. For improved productivity, performing the non-stack interleaf control needs a mechanism for suspending conveyance of a sheet in a conveyance path located between a sheet reversing unit and a position of a pair of registration rollers arranged upstream of an image forming unit in a sheet conveyance direction. Without the mechanism, a long interval is needed between sheets, resulting in lowered productivity of image forming. A large-scale and high-speed image forming apparatus for performing double-sided image forming by using the non-stack interleaf control, in general, has a long conveyance path, thereby resulting in, in particular, lowered productivity.
For such an image forming apparatus to have a shorter interval between sheets, a plurality of waiting positions need to be arranged for a sheet. When an image to be formed includes a great amount of data (e.g. a picture), a sheet waits at a registration position before image forming for a long time. As a result, following sheets may come into conflict with each other.
Another background sheet conveyance apparatus includes a mechanism for causing a plurality of sheets to wait in a conveyance path. Further, a distance between a reverse unit and a registration unit is configured to be greater than 216 mm multiplied by a number of sheets subjected to an interleaf operation. The mechanism includes a plurality of drive units independently driven by respective motors so that the plurality of sheets can be stopped at respective waiting positions.